Integrated circuit (IC) devices have helped to reduce the complexity and size of radio receivers. In particular, AM-FM radios have benefited because virtually all of the active components can be contained in a single IC. A few off-chip mostly passive components are combined with the IC to provide a complete pocket sized AM-FM radio. The greatly reduced size has resulted in bringing the AM antenna, which is usually a ferrite core wire wound inductor, into close proximity with the loud speaker. In order to provide high fidelity (Hi Fi) FM performance, the audio system usually employs a broad band amplifier. Such devices have substantial gain out to about 15 kHz and in the AM broadcast band still have measurable response. When such an amplifier is employed in an AM radio, it can produce substantial audio signal related harmonic energy. While this energy is not heard, it can be radiated and picked up by the nearby AM antenna. Such signals appear in the receiver as noise and can seriously impair the AM radio sensitivity. One solution to this problem is to employ narrow band audio amplifiers, but this degrades the receiver's FM fidelity capability. Another solution is to employ special design amplifiers, usually employing filter circuitry to suppress AM radio noise. This approach is difficult to implement and often results in an unstable amplifier.
Another problem area is the AM-FM mode switching. Many prior art receivers employ a complex multiple-pole-double-throw switch. The various critical functions are simultaneously switched by what is, in effect, a multiple gang switch. Such devices are bulky, expensive and subject to failure. In addition, they often complicate the wiring pattern for the receiver.